Polymers are compounds having a high molecular weight (polymer), and refer to compounds formed through polymerization of several low molecular weight compounds called monomers. Polymers may be divided into linear polymers, branched polymers, crosslinked polymer and the like depending on the chain structures and forms, and show big differences in physical and chemical properties depending on the structures.
Polymers have excellent mechanical strength considering their relatively light weight and have favorable processibility, and have been mainly used as materials forming structures, however, use of polymers as functional materials has recently emerged due to their excellent physical and chemical properties.
Typical examples thereof may include use as a polymer separator. A polymer separator means a polymer membrane having a function of separating materials rather than a simple thin membrane such as films. Specifically, polymers have been used as an electrolyte membrane capable of cation exchange in fuel cells, redox flow batteries and the like.
A fuel cell is an energy conversion device directly converting chemical energy of fuel into electric energy. In other words, a fuel cell employs a power generation method utilizing a fuel gas and an oxidizer, and using electrons generated during the oxidation and reduction reactions of these to produce power. A membrane-electrode assembly (MEA) of a fuel cell is a part where an electrochemical reaction of hydrogen and oxygen occurs, and is formed with a cathode, an anode and an electrolyte membrane, that is, an ion conductive electrolyte membrane.
A redox flow battery (oxidation-reduction flow battery) is a system charged and discharged by active materials included in a liquid electrolyte being oxidized and reduced, and is an electrochemical storage device directly storing chemical energy of the active materials as electric energy. A unit cell of the redox flow battery includes an electrode, an electrolyte and an ion-exchange membrane (electrolyte membrane).
Due to their high energy efficiency and environmental friendly properties of low contaminant emissions, fuel cells and redox flow batteries have been researched and developed as a next generation energy source.
One of core constituents in a fuel cell and a redox flow battery is a polymer electrolyte membrane capable of cation exchange, and properties of 1) excellent proton conductivity, 2) preventing electrolyte cross over, 3) high chemical resistance, 4) strengthening mechanical properties and/or 5) low swelling ratio are favorably required.
The polymer electrolyte membrane is divided into fluorine-based, partial fluorine-based, hydrocarbon-based and the like, and the partial fluorine-based polymer electrolyte membrane has excellent physical and chemical stability due to a fluorine-based main chain, and has an advantage of exhibiting high thermal stability. In addition, in the partial fluorine-based polymer electrolyte membrane, a cation transfer functional group is attached at the end of the fluorine-based chain as in the fluorine-based polymer electrolyte membrane, and therefore, advantages of both the hydrocarbon-based polymer electrolyte membrane and the fluorine-based polymer electrolyte membrane are capable of being obtained.
Researches on monomers used in polymer syntheses have been conducted in order to prepare a polymer membrane for a fuel cell and/or a redox flow battery having high durability and acid resistance. In addition, in order to increase the use of partial fluorine-based polymer electrolyte membranes, researches on partial fluorine-based polymer electrolyte membranes with enhanced proton conductivity, mechanical properties, physical and chemical properties and the like have been ongoing.